lib/percpu_counter.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Fast batching percpu counters.
   4  */
   5
   6 #include <linux/percpu_counter.h>
   7 #include <linux/notifier.h>
   8 #include <linux/mutex.h>
   9 #include <linux/init.h>
  10 #include <linux/cpu.h>
  11 #include <linux/module.h>
  12 #include <linux/debugobjects.h>
  13
  14 #ifdef CONFIG_HOTPLUG_CPU
  15 static LIST_HEAD(percpu_counters);
  16 static DEFINE_SPINLOCK(percpu_counters_lock);
  17 #endif
  18
  19 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
  20
  21 static struct debug_obj_descr percpu_counter_debug_descr;
  22
  23 static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
  24 {
  25         struct percpu_counter *fbc = addr;
  26
  27         switch (state) {
  28         case ODEBUG_STATE_ACTIVE:
  29                 percpu_counter_destroy(fbc);
  30                 debug_object_free(fbc, &percpu_counter_debug_descr);
  31                 return true;
  32         default:
  33                 return false;
  34         }
  35 }
  36
  37 static struct debug_obj_descr percpu_counter_debug_descr = {
  38         .name           = "percpu_counter",
  39         .fixup_free     = percpu_counter_fixup_free,
  40 };
  41
  42 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
  43 {
  44         debug_object_init(fbc, &percpu_counter_debug_descr);
  45         debug_object_activate(fbc, &percpu_counter_debug_descr);
  46 }
  47
  48 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
  49 {
  50         debug_object_deactivate(fbc, &percpu_counter_debug_descr);
  51         debug_object_free(fbc, &percpu_counter_debug_descr);
  52 }
  53
  54 #else   /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
  55 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
  56 { }
  57 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
  58 { }
  59 #endif  /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
  60
  61 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
  62 {
  63         int cpu;
  64         unsigned long flags;
  65
  66         raw_spin_lock_irqsave(&fbc->lock, flags);
  67         for_each_possible_cpu(cpu) {
  68                 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
  69                 *pcount = 0;
  70         }
  71         fbc->count = amount;
  72         raw_spin_unlock_irqrestore(&fbc->lock, flags);
  73 }
  74 EXPORT_SYMBOL(percpu_counter_set);
  75
  76 /**
  77  * This function is both preempt and irq safe. The former is due to explicit
  78  * preemption disable. The latter is guaranteed by the fact that the slow path
  79  * is explicitly protected by an irq-safe spinlock whereas the fast patch uses
  80  * this_cpu_add which is irq-safe by definition. Hence there is no need muck
  81  * with irq state before calling this one
  82  */
  83 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
  84 {
  85         s64 count;
  86
  87         preempt_disable();
  88         count = __this_cpu_read(*fbc->counters) + amount;
  89         if (count >= batch || count <= -batch) {
  90                 unsigned long flags;
  91                 raw_spin_lock_irqsave(&fbc->lock, flags);
  92                 fbc->count += count;
  93                 __this_cpu_sub(*fbc->counters, count - amount);
  94                 raw_spin_unlock_irqrestore(&fbc->lock, flags);
  95         } else {
  96                 this_cpu_add(*fbc->counters, amount);
  97         }
  98         preempt_enable();
  99 }
 100 EXPORT_SYMBOL(percpu_counter_add_batch);
 101
 102 /*
 103  * Add up all the per-cpu counts, return the result.  This is a more accurate
 104  * but much slower version of percpu_counter_read_positive()
 105  */
 106 s64 __percpu_counter_sum(struct percpu_counter *fbc)
 107 {
 108         s64 ret;
 109         int cpu;
 110         unsigned long flags;
 111
 112         raw_spin_lock_irqsave(&fbc->lock, flags);
 113         ret = fbc->count;
 114         for_each_online_cpu(cpu) {
 115                 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
 116                 ret += *pcount;
 117         }
 118         raw_spin_unlock_irqrestore(&fbc->lock, flags);
 119         return ret;
 120 }
 121 EXPORT_SYMBOL(__percpu_counter_sum);
 122
 123 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
 124                           struct lock_class_key *key)
 125 {
 126         unsigned long flags __maybe_unused;
 127
 128         raw_spin_lock_init(&fbc->lock);
 129         lockdep_set_class(&fbc->lock, key);
 130         fbc->count = amount;
 131         fbc->counters = alloc_percpu_gfp(s32, gfp);
 132         if (!fbc->counters)
 133                 return -ENOMEM;
 134
 135         debug_percpu_counter_activate(fbc);
 136
 137 #ifdef CONFIG_HOTPLUG_CPU
 138         INIT_LIST_HEAD(&fbc->list);
 139         spin_lock_irqsave(&percpu_counters_lock, flags);
 140         list_add(&fbc->list, &percpu_counters);
 141         spin_unlock_irqrestore(&percpu_counters_lock, flags);
 142 #endif
 143         return 0;
 144 }
 145 EXPORT_SYMBOL(__percpu_counter_init);
 146
 147 void percpu_counter_destroy(struct percpu_counter *fbc)
 148 {
 149         unsigned long flags __maybe_unused;
 150
 151         if (!fbc->counters)
 152                 return;
 153
 154         debug_percpu_counter_deactivate(fbc);
 155
 156 #ifdef CONFIG_HOTPLUG_CPU
 157         spin_lock_irqsave(&percpu_counters_lock, flags);
 158         list_del(&fbc->list);
 159         spin_unlock_irqrestore(&percpu_counters_lock, flags);
 160 #endif
 161         free_percpu(fbc->counters);
 162         fbc->counters = NULL;
 163 }
 164 EXPORT_SYMBOL(percpu_counter_destroy);
 165
 166 int percpu_counter_batch __read_mostly = 32;
 167 EXPORT_SYMBOL(percpu_counter_batch);
 168
 169 static int compute_batch_value(unsigned int cpu)
 170 {
 171         int nr = num_online_cpus();
 172
 173         percpu_counter_batch = max(32, nr*2);
 174         return 0;
 175 }
 176
 177 static int percpu_counter_cpu_dead(unsigned int cpu)
 178 {
 179 #ifdef CONFIG_HOTPLUG_CPU
 180         struct percpu_counter *fbc;
 181
 182         compute_batch_value(cpu);
 183
 184         spin_lock_irq(&percpu_counters_lock);
 185         list_for_each_entry(fbc, &percpu_counters, list) {
 186                 s32 *pcount;
 187
 188                 raw_spin_lock(&fbc->lock);
 189                 pcount = per_cpu_ptr(fbc->counters, cpu);
 190                 fbc->count += *pcount;
 191                 *pcount = 0;
 192                 raw_spin_unlock(&fbc->lock);
 193         }
 194         spin_unlock_irq(&percpu_counters_lock);
 195 #endif
 196         return 0;
 197 }
 198
 199 /*
 200  * Compare counter against given value.
 201  * Return 1 if greater, 0 if equal and -1 if less
 202  */
 203 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
 204 {
 205         s64     count;
 206
 207         count = percpu_counter_read(fbc);
 208         /* Check to see if rough count will be sufficient for comparison */
 209         if (abs(count - rhs) > (batch * num_online_cpus())) {
 210                 if (count > rhs)
 211                         return 1;
 212                 else
 213                         return -1;
 214         }
 215         /* Need to use precise count */
 216         count = percpu_counter_sum(fbc);
 217         if (count > rhs)
 218                 return 1;
 219         else if (count < rhs)
 220                 return -1;
 221         else
 222                 return 0;
 223 }
 224 EXPORT_SYMBOL(__percpu_counter_compare);
 225
 226 static int __init percpu_counter_startup(void)
 227 {
 228         int ret;
 229
 230         ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
 231                                 compute_batch_value, NULL);
 232         WARN_ON(ret < 0);
 233         ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
 234                                         "lib/percpu_cnt:dead", NULL,
 235                                         percpu_counter_cpu_dead);
 236         WARN_ON(ret < 0);
 237         return 0;
 238 }
 239 module_init(percpu_counter_startup);